@media screen and (max-width: 599px) {

    .master-header, .mobile-only { visibility:hidden; display:none; }
    .show-nav .master-header, .mobile-only { visibility:visible; display:block; }
    .show-nav .master-container,
    .show-nav .master-footer,
    .show-nav .logo-mobile,
    .show-nav .menu-mobile { margin-left:260px; }
}